A.4 conservation of biodiversity

1. Types of biodiversity

The word biodiversity (biological diversity) is the variety

• Species diversity-the many different species on

of life in all its forms, levels and combinations.

the evolutionary tree of life. These species have

• Ecosystem diversity-variety in the combinations of

varied body plans, internal structure, life cycles and

species living together in communities. This diversity

modes of nutrition.

is partly due to the very varied environments on Earth

• Genetic diversity within species-variety in the

and the geographical ranges of organisms.

gene pool of each species. There is variation between geographically separated populations and within populations.

3. Anthropogenic causes of the sixth mass extinction

A sixth mass extinction of species is underway. The causes are all anthropogenic (due to human activities).

Three case studies of extinction are described here.

Local case studies should also be studied:

1. Caribbean monk seal—a marine mammali

Neomonachus

tropicalis was

native to the warm temperate and

tropical waters of the Caribbean Sea and

western Atlantic, but has not been sighted for over 70 years. It was hunted for its oil through the 18th and

19th centuries. The Caribbean monk seal was an easy target because of its need to breed on beaches, where it was slow-moving and lacking in fear of humans.

A second factor was overfishing of the coral reefs where the seals fed, leading to starvation.

2. Giant moa-part of terrestrial megafauna

Dinornis novaezealandiae, had a height of up to 3.6 m and mass of 230 kg. It was native to the north island of New Zealand, which remained uninhabited by humans until the 13th century, when Polynesian settlers became the Mãori iwi. It then took less than 200 years for the giant moa to be hunted to extinction, for meat.

Overharvesting was the main cause of extinction in these three case studies-the species was exploited at a faster rate than it could replace lost individuals by reproduction.

There are other common causes of extinction:

Habitat destruction

Natural habitats (such as forests or grasslands) have been destroyed, leading to species extinctions. Agriculture is the main cause, with over 13 billion hectares of land now cultivated or used for rearing livestock. Natural habitats have also been destroyed to build towns and cities.

Invasive species

When alien species are introduced to ecosystems, they can drive native species to extinction by predation, spreading of pests and diseases, or competition for resources. Endemic species become extinct if they hybridize with alien species.

Pollution

Chemical industries produce a vast range of substances that are used and then discarded in the environment.

Burning of fossil fuels, agriculture, mining, oil extraction and pharmaceuticals are all major sources of pollutants.

Rothschild, R.L.W. (1907) Extinct birds.

London: Hutchinson.

3. Silphium-an early plant extinction

This plant grew in Libya and probably became extinct within a few hundred years of the arrival of ancient Greeks, who harvested it for use as a birth control agent. Overgrazing and desertification may have also contributed.

Global climate change

Human activities are currently causing very rapid changes in temperature, rainfall and other climatic variables.

Species that fail to adapt quickly enough or cannot migrate face extinction. 2. Comparing current number of species on Earth with past numbers

Estimates of the number of species currently inhabiting

The effects of speciation and extinction on biodiversity

the Earth vary widely. Most are between 2 and 10 million.

are explained in Section A4.1.6. There have been five

It is even more difficult to estimate how many species

mass extinctions when many species disappeared. The

lived on Earth in the past, but relative levels of biodiversity most recent was 66 million years ago at the end of the

can be deduced from fossil evidence. This shows much

Cretaceous period, when a huge asteroid collided with

variation. The graph shows an example of such data.

the Earth. The consequent environmental disruption caused many species to die out, including all non-avian

spewue

of marine

siaqwnu

dinosaurs. The previous four mass extinctions were due

5,000 ÷

to volcanic activity and major changes to the atmosphere

4,000 -

and global climate. Biodiversity tends to rise gradually between mass extinction events, with new forms of life evolving. For example, the extinction of the non-avian dinosaurs and other groups at the end of the Cretaceous period was followed by the evolution of many new species

1,000 -

of birds and mammals.

There have been no mass extinction events for 66 million years. As a result, biodiversity is probably higher now than it has ever been.

NOS

542 500 450 400 350 300 250 200 150 100 50 0

millions of years ago

5. The biodiversity crisis

Journalists use the term "biodiversity crisis" to describe Surveys can also give evidence of change in an the unprecedented losses of ecosystems and species

ecosystem for these variables:

occurring today. As scientists, we must always look for • species diversity evidence before making a claim.

• richness and evenness of biodiversity

In this case we need evidence of losses before declaring that there is indeed a biodiversity crisis. One of many sources of evidence is IPBES (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services).

  • area occupied

  • extent of ecosystem degradation.

Surveys can also provide evidence for a taxonomic group:

• number of threatened species within the group.

Evidence can be gathered directly by carrying out reliable surveys. If repeated, surveys can provide evidence of change in these variables in a species:

  • numbers in populations of the species

  • genetic diversity

  • range of the species.

Although expert scientists play a key role in monitoring biodiversity and identifying the most serious threats, there are opportunities for all citizens to contribute. This is an example of what is often called "citizen science".

Some of the most useful data has been collected by individuals who have monitored a population or an ecosystem regularly over many years.

Patterns and trends

Scientists analyse their observations, looking for patterns or trends. Classification is an example of pattern recognition but the same observations can be classified in different ways. For example, "splitters" recognize more species than "lumpers" in any taxonomic group. This makes it impossible to be sure how many species of living organism there are on Earth today. In 1857, after analysing the numbers of species and varieties per genus in different taxonomic groups, Charles Darwin referred to "hair-splitters & lumpers". His conclusion was that "varieties are only small species-or species only strongly marked varieties". Do you agree?

Evidence

It is now easy to generate fake text using Al, so it is more important than ever to have evidence for claims. In science it is essential.

• The evidence must be verifiable, so it must usually come from a trusted published source and have been peer-reviewed (checked by other scientists).

It must be clear how the evidence was obtained (methodology). Data recorded by citizens rather than scientists is often very valuable, but the methodology must be rigorous. 4. Ecosystem loss due to anthropogenic causes

If environmental conditions change, the replacement of one ecosystem by another is natural. This has happened repeatedly over the past 2.6 million years due to alternation between glacials and interglacials (warmer and colder periods). However, there has been an unprecedentedly rapid loss of ecosystems during the past few centuries and the causes are anthropogenic.

Two case studies of ecosystem loss are described here but local examples will also be worthy of study.

1. Mixed dipterocarp forest of southeast Asia

Dipterocarps are a family of about 700 species of tropical hardwood tree. They used to dominate large areas of rainforest in southeast Asia. Mixed dipterocarp forest (MDF) has an extremely high diversity of dipterocarp and other tree species. On the island of Brunei, for example, there are 20 native dipterocarp species. Small areas of MDF often contain 10 or more of these. The highest diversity of tree species tends to occur on nutrient-poor sandy soils.

MDF typically has particularly high quantities of merchantable timber per hectare so it has been widely targeted for logging, both legal and illegal. Since the 1970s, most areas of MDF have been lost; undisturbed areas are now largely found in upland sites where access is more difficult. Areas of MDF that have suffered the greatest losses are on lowland sites, especially where nutrient-rich soils overlie deep peat. Large areas have been lost due to land conversion to palm oil plantations.

This is particularly unfortunate as the peat in these areas, formed over the past 4,000-5,000 years, can be up to 15 m deep. This peat can store 250 tonnes of carbon per hectare. Drainage during conversion to palm oil plantations causes the peat to decompose, releasing CO, into the atmosphere. This contributes to another threat: rising sea levels caused by global warming will flood deep-peat lowland areas with seawater, destroying what little MDF remains there.

2. Loss of the Aral Sea-an ecological disaster

The Aral Sea, between Kazakhstan and Uzbekistan, was the fourth largest lake in the world. It was fed by rivers but had no outflows, with water only removed by evaporation.

As a result, the salinity was higher than in a freshwater lake.

In the 1960s, a major water management scheme diverted two major rivers that fed the Aral Sea in order to irrigate an area of desert. This led to falling water levels and much of the former lake is now desert.

Apart from the reduction in the area and depth of the lake, the increase in the water salinity was a major contributor to ecosystem collapse. In some of the remaining parts of the lake, salinity has risen from 1% to more than 22%, compared with about 3.5% for normal seawater. A total of 24 species of fish were endemic to the Aral Sea, all of which are now extinct. Most invertebrate species have also disappeared. The NASA satellite images show the extent of the Aral Sea in 1989 (left) and 2014 right.

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Eight categories of direct or indirect cause of ecosystem loss are outlined here:

  1. Agriculture the main cause of ecosystem loss. Most temperate forests and grasslands (such as the prairies of North America) were cleared before the 1970s.
    Since then, much tropical forest has been lost.

  2. Urbanization-building of homes, offices and factories, together with associated infrastructure of roads and railways. This has been inevitable given the rapid and continued rise in the human population.

  3. Overexploitation of natural resources-such as gathering of fuel wood, hunting of animals for bushmeat and fishing. Loss of a single keystone species can threaten whole ecosystems. Overfishing on the Canadian Grand Banks is explored in Section D4.2.6.

  4. Mining and smelting-opencast mines destroy areas of natural ecosystem entirely. Smelting and disposal of waste from mining can cause pollution and more widespread damage. Much tropical rainforest has been lost due to mining.

  5. Water management-reservoirs created by building dams can flood natural ecosystems. Extraction of water for irrigation and for industrial or domestic use can greatly reduce river flows. For example, the Colorado River no longer reaches the sea.

  6. Drying of wetlands-swamps and other wetlands are drained for conversion to agriculture. This is explored for HL in Section D4.2.15. Wetlands are also destroyed by diverting the water that flowed into them for human use.

  7. Leaching-washing of fertilizers into rivers and lakes causes eutrophication and algal blooms.
    Oligotrophic ecosystems, in which organisms are adapted to low nutrient concentrations, have been lost. This is explored in Section D4.2.8.

  8. Climate change-anthropogenic climate change is the most common cause of loss. Relationships between ecosystem types and climate are further explored in Theme B and the likely future effects of climate change are considered in Theme D. 6. The biodiversity crisis-causes

    Species extinction is a natural process but current rates are 100-1,000 times higher than normal and are rising.

    A biodiversity crisis has been developing since about

    1970. The causes (also discussed in Sections A4.2.3 and A4.2.4) are:

    • hunting and other forms of over-exploitation

    • urbanization, with towns and cities growing ever larger

    • deforestation and clearance of land for agriculture, leading to loss of natural habitats

    • pollution of land and sea throughout the world

    • alien invasive species spread by global transport / movement or deliberate introductions. Such species may be pests, cause disease or compete with native species.

    Humans have been causing species extinctions for thousands of years, and none of these causes are new, but their intensity has increased

    A Dipterocarp forest-rich in biodiversity but much has been lost.

    significantly over

    the last 100 years. This is a consequence of the enormous rise in the number of people on Earth. Between 1920 and 2020 the human population more than quadrupled, from less than two billion to almost eight billion. Overpopulation is the overarching issue that makes human activities a threat to most other species and risks widespread ecosystem collapse.

    7. Conservation of biodiversity

    No single approach to tackling the biodiversity crisis will be enough. Measures must be selected according to the target species or ecosystems and the causes of biodiversity loss.

    In situ conservation leaves species in their natural habitats. Ideally, large areas of the Earth's surface remain as pristine wilderness, but partially degraded areas can still become valuable nature reserves or national parks. With in situ conservation, species live in the abiotic environment to which they are adapted, interacting with other wild species, so they remain adapted to their ecological niches and the integrity of whole ecosystems is conserved.

    There is often a need for management of nature reserves. This could involve the removal of alien species, reintroduction of locally extinct species, control of population sizes, control of access by humans and prevention of poaching.

    Pangolins are being poached in huge numbers from forests in Africa and Asia

    8. The EDGE of Existence programme

    The EDGE of Existence project uses two criteria to identify animal species that are most deserving of conservation.

    • Evolutionarily Distinct: does the species have few or no close relatives, so it is a member of a very small clade?

    • Globally Endangered: Is the species likely to become extinct because all remaining populations are threatened?

    Species that fit both criteria (EDGE species) are listed and targeted for intense conservation efforts. Some species are the last members of a clade that has existed for tens or hundreds of millions of years and it would be tragic for them to become extinct as a result of human activities.

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    Some ecosystems are so damaged that major intervention is needed. The process of rewilding is the return of degraded ecosystems to as natural a state as possible. Recovery can be remarkably rapid and balance is then maintained by natural ecological processes instead of human intervention.

    Ex situ conservation is preservation of species outside their natural habitats. The initial step is removal of individuals from the wild. Traditionally, plant species are then grown and propagated in botanic gardens and animals are kept and bred in zoos with the ultimate aim of releasing captive-bred individuals in their native habitats. Ecosanctuaries are now being set up on islands or in large fenced areas with semi-natural conditions but predator control.

    A more radical approach to ex situ conservation is the long-term storage of germ plasm (living material that could be used for propagation in the future). Seeds of plants are stored dry in seed banks at low temperatures (around -20°C), so they can maintain viability for long periods. Animal germ plasm (samples of tissue, eggs or sperm) is stored at temperatures of between -20 and -200°C, in tissue banks.

    Global impacts of science

    Prioritization of one species for conservation efforts and not another has consequences, with complex ethical, environmental, political, social, cultural and economic implications. Scientists therefore have an obligation to ensure that such issues are debated. The preparation of lists of EDGE species is part of the